The present invention relates to light source apparatuses, which are used in image display apparatuses such as head mounted displays (HMDs) and illuminate image-forming elements such as reflective liquid crystal panels.
Conventional HMDs, which includes a transmissive liquid crystal panel with color filters, use a cold-cathode-tube type white flat light source to illuminate the liquid crystal panel.
In contrast, many recent HMDs use a light source capable of emitting light of three (RGB) colors and adopt a color-sequential displaying method in which images on the liquid crystal panel are rewrite in accordance with a light-emission switching timing of the light source.
Moreover, color LEDs are often used as a light source of HMDs. The color LED has three light-emitting portions of RGB, and the emission color and emission intensity of the LED can be electrically controlled.
In such light source apparatuses, two to four LEDs are often placed on a side face of the apparatus chassis. Such a side-face LED placement is effective for thinning flat light source apparatuses, but unsuitable for high-intensity light sources since many LEDs cannot be placed on the side face.
Adopting a so-called bottom LED placement that has been disclosed in Japanese Patent Application Laid-Open No. 2004-311353 makes it possible to place many LEDs to enable high light intensity. In the bottom LED placement, many LEDs whose light-emitting surfaces face the direction of the emergent surface of the light source apparatus are placed on the bottom of the apparatus chassis.
The light source apparatus disclosed in Japanese Patent Application Laid-Open No. 2004-311353 uses LEDs (bullet-shaped LEDs) with a domed lens whose light radiation angle is narrow to reduce unevenness of luminance and color on the emergent surface (or, the light source surface), which is a defect of the bottom LED placement. Further, in the above-mentioned light source apparatus light from the LEDs is reflected by two reflecting plates and then diffused by a diffusing plate. This achieves a thin light source apparatus capable of reducing unevenness of luminance and color.
A liquid crystal panel needs to be illuminated with linearly polarized light (P-polarized light or S-polarized light). Therefore, a polarizer is provided in light source apparatuses.
However, common polarizers transmit light with a polarization direction corresponding to the polarizing axis direction thereof and absorb light with a polarization direction different from the polarizing axis direction. Accordingly, using a common polarizer for obtaining linearly polarized light reduces the amount of light from the LEDs and therefore it is difficult to increase the light intensity without changing the number of LEDs or with reduction thereof.